In recent years, carbon fiber-reinforced composite materials including carbon fibers as reinforcing fibers, because of having high specific strength and high specific modulus, have been used in applications including structural materials of aircraft, automobiles, and the like, sports goods such as tennis rackets, golf shafts, and fishing rods, and general industrial uses.
Methods of producing the carbon fiber-reinforced composite material include a method in which a prepreg, a seat type intermediate material obtained by impregnating reinforcing fibers with an uncured matrix resin, is cured, and resin transfer molding in which a liquid resin is injected into reinforced fibers placed in a mold to prepare an intermediate, and the intermediate is cured. Of these production methods, in the method using prepreg, a carbon fiber-reinforced composite material is produced typically by laminating several sheets of prepreg and then applying heat and pressure to the laminate. As the matrix resin in the prepreg, thermosetting resins, in particular, epoxy resins are often used in terms of productivity, e.g., processability.
Particularly in applications of structural materials of aircraft, automobiles, and the like, properties required for the carbon fiber-reinforced composite material have recently been becoming stricter with its increasing use, and a high tensile strength and a high compression strength have been required. However, there is often a trade-off between the tensile strength and the compression strength of the carbon fiber-reinforced composite material, and it has been very difficult to achieve the tensile strength and the compression strength both at a high level.